Fluorescent lamp with variable deformation in envelope

ABSTRACT

A fluorescent lamp having at least one groove therein which is rotated on a curved path around and along the longitudinal axis of the lamp and which varies in depth.

United States Patent Inventor Joel Shurgan Washington Township Bergen County, NJ. Appl. No. 768,618 Filed Oct. 15, 1968 Patented Feb. 2, 1971 Assignee Duro-Test Corporation Bergen, NJ. a corporation of New York Continuation of application Ser. No. 660,152, July 20, 1967, Continuation of application Ser. No. 453,643, May 6, 1965, now abandoned.

FLUORESCENT LAMP WITH VARIABLE DEFORMATION IN ENVELOPE 21 Claims, 12 Drawing Figs.

US. Cl 313/109,

[51] lnt.Cl ..H0lj61/30, H0 1 j 61/35 [50] Field ofSearch 313/182, 109, 220, 317; 220/21; D26/8; 313/204 [56] References Cited UNITED STATES PATENTS 13. 981268 5/1964 Thorington et a1. D26/8 2,950,410 8/1960 Lemmers et a]. 313/109 Primary Examiner-J0hn Kominski Assistant Examiner-Palmer C. Demeo Attorney-Darby & Darby ABSTRACT: A fluorescent lamp having at least one groove therein which is rotated on a curved path around and along the longitudinal axis of the lamp and which varies in depth.

PATENTED FEB 2197! SHEET 1 BF 3 mvamm JOEL SHURGAN Y 49%, {496% ATTORNEYS PATENTEU FEB 2 l97| SHEET 2 BF 3 INVENTOR. JOEL SHURGAN W 49% f/xQm ATTOR N EYS PATENTED FEB 2191: 3.560.786

SHEET 3 OF 3 IMVENTOR JOEL SHURGAN FLUORESCENT LAMP WITH VARIABLE DEFORMATION IN ENVELOPE This application is a continuation of application Ser. No. 660,152, filed July 20, I967, and now abandoned, which application is, in turn, a continuation-in-part of application Ser. No. 453,643, filed May 6, I965. and now abandoned.

This invention relates to lamps of the arc discharge type and more particularly to a fluorescent lamp having a deformation therein to produce increased length for the arc stream.

In the copending application of Luke Thor-ington et al., Ser. No. 441,411, filed Mar. II, 1965. entitled Continuous Non Circular Cross Section Lamp and of which I am a coinventor. which application is a continuation of application Ser. No. 124,505 filed July 17, 1961 now abandoned, which application is in turn a continuation-in-part of application Ser. No. 50,265, filed Aug. 17, 1960 now abandoned, both of which applications are assigned to the same assignee, a fluorescent lamp is described in which a noncircular cross section is provided. This non circular cross section is produced by one or more grooves or deformations in the envelope of an originally generally tubular lamp, each groove or deformation being rotated on a respective curved path around and along the Iongitudinal axis of the envelope. In the preferred embodiment of the invention the curved path is a helix.

As described in the aforegoing copending applications, a lamp of this type has several advantages. One of these is the ability to obtain a desired noncircular cross section substan tially throughout a large portion of the overall length of the lamp envelope for increasing the efficiency of plasma opera tion while still maintaining adequate structural strength for the lamp envelope. Even though the envelope is deformed, it still retains overall general cylindricity to enable it to be readily bundled, rolled, and coated with a phosphor. An additional advantage of a lamp of this type is that rotation of the noncircular cross section in a curved path along the length of the envelope causes the arc stream to follow a longer path. This produces a higher voltage gradient for the lamp. All of the aforesaid advantages contribute to a lamp having good structural characteristics and increases efiiciency that is able to provide higher wattage loadings per unit length of lamp than fluorescent lamps with conventional cylindrical envelopes.

The present invention is also directed to a fluorescent lamp of the type having at least one groove in the wall thereof for the purposes of producing a desired noncircular cross section and at the same time increasing the arc stream length. In accordance with the present invention, an envelope is provided having one or more grooves or deformations therein which are formed in the envelope in a curved path around and along the longitudinal axis thereof. I-Iere, however, the depth or another dimension of a groove is varied thereby producing a noncircular cross section of changing shape.

Where the depth of the noncircular cross section is changed as the groove is rotated in a curved path around and along the longitudinal axis of the envelope, the arc stream not only follows the curved path but its center is also deflected transverse to the longitudinal axis of the envelope in accordance with the varying depth of the groove. Thus, the arc path is lengthened both by the rotation of the groove along a curved path as well as in a direction transverse to the axis. For an equivalent length straight envelope or one having only deformations of uniform depth, a longer are stream will be obtained with the envelope of the present invention.

In one embodiment of the present invention a lamp envelope having two grooves therein is provided and both of these grooves have variable depths throughout their lengths. In one form of this embodiment, the depth of the two grooves preferably vary in an opposite manner (out of phase) so that as the depth of a portion of one groove is increasing the depth of the portion of the other groove opposite the first is decreasing. By doing this, the arc stream is still deflected off the envelope axis. Also, the perimeter to area ratio of the envelope at any cross section thereof taken through a plane diametrical to its longitudinal axis is held substantially constant. This increases the plasma operating efficiency. In another form of this embodiment. the depths of the two grooves change in the same manner (in phase) to produce areas of relatively small cross section where the wall losses are increased.

It is therefore an object of the present invention to provide an improved fluorescent lamp having a groove therein which is rotated on a curved path around and along the longitudinal axis of the envelope with a dimension of the groove varying in a predetermined manner.

Another object is to provide an improved fluorescent lamp having at least one groove in the envelope which is rotated on a curved path around and along the longitudinal axis of the envelope with the depth of the groove being varied in a predetermined manner as it is rotated.

A further object is to provide an envelope for a fluorescent lamp having a pair of grooves therein, the depths of each of the grooves being varied in a predetermined manner so that a substantially constant perimeter to area ratio for the envelope is maintained at any cross section thereof.

An additional object is to provide a lamp having a pair of grooves therein where depths vary substantially in phase with one another.

Another object is to provide an envelope for a fluorescent lamp having a pair of grooves therein with each of the grooves being rotated on a separate curved path around and along the longitudinal axis of the envelope and with the depths of the grooves being varied.

An additional object is to provide a fluorescent lamp envelope having two grooves therein which produce a desired noncircular cross section, with each of the grooves being rotated in a separate curved path around and along the longitudinal axis of the envelope while at the same time having their depths vary in opposite directions to maintain a substantially constant perimeter to area ratio.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which:

FIG. I is a perspective view of a fluorescent lamp shown partially broken away made in accordance with the invention having one groove therein rotated around the envelope with the depth of the groove being varied;

FIGS. 2, 3 and 4 are cross sections of the lamp envelope of FIG. 1 taken along lines 2-2, 3-3 and 4-4' respectively;

FIG. 5 is a persepective view of another embodiment of the invention shown partially broken away having a pair of grooves therein whose depths vary;

FIG. 6 is an enlarged perspective view of a portion of the lamp of FIG. 2; and

FIGS. 7, 8 and 9 are cross sections of the lamp envelope of FIGS. 2 and 3 taken along lines 7-7, 8-8 and 9-9 respectively of FIG. 2.

FIGS. 10, 11 and 12 are cross sections of another embodi ment of lamp, at envelope positions similar to those of FIGS. 7, 8 and 9.

FIG. I shows a fluorescent lamp 10 having a generally overall cylindrical envelope 11. This envelope has the normal phosphor coating 13 on the interior wall thereof together with an ionizable medium therein (not shown), usually a small quantity of mercury and an inert starting gas. Envelope 11 is shouldered down at each end 15 to accommodate an end cap 16 on which is mounted a respective electrode 18. The par ticular type of electrode used, as well as the types of phosphor, ionizable medium, and starting gas are conventional in the art and any suitable one or combinations thereof may be selected. These, in themselves, form no part of the present invention.

The envelope 11 has a single groove or deformation 20 formed therein in a curved path along and around the envelope longitudinal axis. The groove 20 can be of any desired shape for example, any type of a conic section such as a por tion of a circle, parabola or hyperbola. An irregularly shaped curve may also be used.

It should be understood that wherever a groove 20 is present in the envelope 11 that the envelope has a noncircular cross section in a plane taken diametrically through its longitudinal axis. In the present invention the groove. and the noncircular cross section produced thereby. is rotated along a curve which is advanced along the length of the envelope. In the preferred embodiments of the invention. the curved path describes a helix. A complete 360 rotation of the curve around the longitudinal axis of the envelope is designated as one pitch of the helix.

In accordance with the invention, the groove has a variable depth as it advances along the length of the envelope. For purposes of illustration a repeating. or periodic. and continuous variation of groove depth is described since this arrangement permits easier fabrication of the lamp. However. any type of depth variation may be utilized in any desired periodic or nonperiodic function and the depth variation need not be continuous.

In any one pitch of the groove 20 around and long the envelope the groove has N cycles of the depth varying function. where N is any fraction or integer. A complete cycle of depth variation means that the groove goes from minimum to maximum depth and then back to minimum depth again. For the purposes of illustration, N is equal to four in FIG. 1 so that there are four complete cycles variations of the depth of the groove 20 in one pitch. It should be understood that the number of cycles can be selected as desired in accordance with the generating function for the depth variation and that the pitch of the groove can be selected as desired.

FIGS. 2 through 4 show cross sections of the lamp envelope of FIG. 1. FIG. 2 shows a cross section where the depth of the groove is at a minimum; FIG. 3 shows a cross section where the depth is approximately half way between minimum and maximum; and FIG. 4 shows the depth of the groove at a maximum. It should be understood that these cross sections repeat themselves cyclically in an alternating pattern, that is FIG. 2, FIG. 3, FIG. 4, FIG. 3, FIG. 2, FIG. 3, FIG. 4 etc. Also, the variation in depth is preferably a continuous one between minimum and maximum points throughout the length of the envelope.

In operation of the lamp of FIGS. 1-4, an arc stream discharge is struck between the two electrodes 18 at opposite ends of the envelope. Since the arc stream generally seeks to travel the path of least resistance, that is through the widest available portion of the envelope, it will travel in a curved path along the length of the envelope in that portion of the envelope cross section where a groove does not exist. In the embodiment of FIG. I, the arc stream travels a helical path. At the same time the arc stream travels the helical path it also moves back and forth transverse of the longitudinal axis of the envelope toward and away from the axis in accordance with the variation in the depth of the groove. For example when encountering the minimum groove depth cross section of FIG. 2, the are stream is most nearly symmetric with the longitudinal axis but is deflected slightly to the right of the envelope due to the presence of groove 20. In the cross section of FIG. 3, the arc stream has rotated slightly due to the rotation of the groove and it is also deflected more off the envelope axis toward the circular portion of the envelope wall. In the cross section of FIG. 4, the arc stream has rotated still further and it is deflected still further off the axis toward the circular portion of the envelope wall due to the further increased depth of the groove. As the depth of the groove decreases the arc stream moves to position more nearly symmetrical with the longitudinal axis, that is, it moves back toward the axis.

Therefore the arc stream follows both a curved path and a generally zigzag or serpentine path at the same time. The latter is due to the variable depth of the groove which deflects the are stream onsequently the total length of the arc stream is increased beyond the length of the envelope by factors corresponding to the pitch of the curved path and the amount of deflection caused by the variable depth groove. The increased arc stream lengthas well as the use of the envelope noncircula'r cross section permits higher wattage per-unit length loading of the lamp than would be possible if the lamp were only cylindrical and without a groove or if the depth of the groove does not vary.

FIGS. 5 through 9 show another embodiment of a lamp made in accordance with the present invention utilizing two grooves or deformations in the lamp envelope. Here, the two grooves 30 and 31 are used each being of generally the same configuration as the groove shown in the lamp of FIGS. 1 through 4. N is also equal to four, approximately, here. Each groove is rotated around and along the longitudinal axis of the envelope in a separate curved path, which illustrativcly shown as being a helix. The center of each curved path is spaced apart by approximately 180 around the circumference of the envelope. Of course, another angular spacing may be used for the groove centers.

As shown, the depth varying function of one of the grooves is advanced with respect to the other by I", that is, one half cycle. Therefore, as thedepth of one groove reaches a maximum at one point the depth of the other groove at the same point on a plane diametrically through the longitudinal axis of the envelope is at a minimum. If the depths of the two grooves 30 and 31 vary in accordance with the same function and at the same periodicity, a relationship of the two grooves is obtained throughout the length of the envelope wherein the depth of one groove is increasing as the depth of the other groove is decreasing, and vice versa. Of course, there is a point in each cycle of groove depth variation in the case where the depth of each groove varies in accordance with the same function, where the depths of the two grooves are equal if they are advanced by l80 with respect to each other. This is explained in more detail below.

FIG. 7 shows a cross section of the lamp of FIGS. 5 and 6 at a point where groove 30 has minimum depth and the portion of groove 31 on the diametric plane has maximum depth. As both grooves advance along the helical curved path fi'om left to right on the drawing from the line 7-7, the depth of groove 31 decreases while the depth of groove 30 increases. A point is reached where the depths of both grooves are the same in a cross-sectional plane. This is shown in FIG. 8. Going still further along the lamp to the right, past the point where the depths of the two grooves are equal, the groove 31 continues to decrease in depth while the depth of groove 30 continues to increase. A point is reached where the groove 31 has minimum depth and the groove 30 has maximum depth. This is shown in the cross section of FIG. 9. The functions start to reverse at this point so that the depth of groove 30 starts to decrease while the depth of groove 31 starts to increase.

In a preferred embodiment of the two groove lamp shown in FIGS. 5-9, the depth varying functions are preferably chosen so that one groove increases in depth by the same amount that the other groove decreases, and vice versa.

This provides an additional advantage over the embodiment of lamp shown in FIGS. 1 through 4 of maintaining a substantially constant perimeter to area ratio for the envelope at any two diametric planes along the envelope length where the grooves exist. Maintaining the same perimeter to area ratio is advantageous since it increases the operating efficiency of the plasma.

Considering nowthe operation of the lamp of FIGS. 5 through 9, an arc stream discharge is struck between the two electrodes at the opposite ends of the lamp. As in the lamp of FIG. I, the are stream travels the curved path formed by the two grooves 30 and 31 around the lamp axis. The are stream is also deflected off axis by the varying depths of the grooves. At the point in the envelope shown in the cross section of FIG. 8, the lamp cross section is generally symmetric and the center of the arc stream is substantially coincident with the longitudinal axis of the envelope. At the point in the envelope illustrated by the cross section of FIG. 7, the arc stream is deflected the maximum distance towards the right of the longitudinal axis since groove 31 has its maximum depth here. Similarly, at the point in the lamp envelope shown by the cross section of FIG. 9, the arc stream is deflected the maximum distance away from groove 30 toward 31 since groove 30 has its maximum depth here. Lesser degrees of deflection are produced on either side of the axis, depending upon which groove is deeper, at other points along the envelope. Thus, the arc stream follows both a curved path and a generally serpentine path as it advances along the length of the tube in accordance with the variation in the depths of the two grooves. The combined lengthening effect of the curved path and the serpentine path produces an arc stream which is considerably longer than the physical length of the envelope 11.

FIGS. 10. 11 and 12 show cross sections of another embodiment of lamp with N=4 at points along an envelope (not shown fully) corresponding to 7-7. 8-8 and 9-9 of FIG. 5. While the depth variation of the two grooves of the lamp of FIGS. 5-9 was 180 out of phase. in the lamp of FIGS. 10-12 they are in phase. That is. the depths of the opposite grooves vary so that when one is at a maximum the other is at a maximum. This is shown in FIGS. 10-12 where in FIG. 10 the opposing grooves 40 and 41 are at or near minimum depth; in FIG. 11 the depths have increased by the same amount to the same depth at an intermediate depth; and in FIG. 12 the depths of the grooves are the same at maximum. This variation repeats as described previously from maximum to minimum, etc. As seen, the grooves also rotate in the same manner as previously described along a helix.

As seen, there is no deflection of the arc stream off the longitudinal axis in the embodiment of FIGS. 10-12. A cross section of varying area is maintained along the length of the lamp. More importantly, in areas of more narrow dimension, such as the narrowest portion shown in FIG. 12, the arc stream is squeezed, increasing the wall losses. This increases the plasma efficiency, as described in the aforesaid copending applications.

While the two embodiments of FIGS. 5-9 and FIGS. 10-12 are shown with 180 out of phase and in phase depth variations for the opposing grooves, it should be understood that a value of out of phase variation between 0 and 180 can also be utilized. Thus, for example, the variations in depth of two opposing grooves varying at the same function can lead or lag by 90, or some other value between 0 and 180. This arrangement would give both deflection off the envelope longitudinal axis and narrowing of the cross-sectional area of the envelope at selected places along the envelopes length. Since the length of the arc stream affects the voltage gradient of the lamp and the cross-sectional area the lamp current, a selection of the phase lead or lag angle is made to produce a desired voltage and current.

As shown in each of the drawings the width of the groove also changes in accordance with the depth. More particularly the drawings illustrate that as the depth decreases the width of the groove increases. While this is the easiest way of forming a glass envelope with the desired groove or grooves, it does not necessarily have to be done this way and a constant width groove may be used for any depth of groove or any variation in width may be utilized as desired together with the depth variation.

As pointed out before, any desired function may be utilized for the variation in depth of the groove or grooves of the lamp. While the functions shown in the accompanying drawings are generally periodic and regular, that is, the depth of the groove is changing more or less continuously, it should be understood that this need not be the case. For example, the grooves can be made with portions thereof of the the same depth. However, this arrangement will not produce the continuous deflection of the arc stream from the axis produced by a continuously changing groove depth.

It should also be understood that in both embodiments of the lamp described that the envelopes still maintain general overall cylindricity. By this it is meant that the grooves or deformations placed in the envelope wall do not in any way destroy the cylindrical overall shape of the envelope and the envelope is still free toroll. Therefore, the lamp can be rolled, and bundled and easily coated with a phosphor during the manufacturing process.

While lamps with only one and two grooves have been shown, it should be understood that lamps having three or more grooves of varying depth can be constructed. In the case of three grooves it is preferred to have the depths of two grooves increasing while the depth of the third groove is decreasing, or vise versa, so a constant perimeter to area ratio can be maintained.

While preferred embodiments of the invention have been described above, it will be understood that these are illustrative only, and the invention is limited solely by the appended claims.

Iclaim:

1. A fluorescent lamp comprising:

an elongated generally tubular envelope formed with a deformation in its outer wall in a curved path of finite radius around the central axis of the envelope and along the major part of the length thereof, said deformation having a finite minimum depth throughout its entire length exclusive of its ends and varying in depth from said minimum at portions thereof along its length,

a quantity of an ionizable material within said envelope, and

electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said are stream discharge following the curved path of said deformation along the length of the envelope and also being deflected from the envelope central axis in. accordance with the variation in depth of the deformation.

2. A lamp as set forth in claim 1 wherein the depth of the deformation varies in accordance with a predetermined recurring function.

3. A fluorescent lamp as in claim 1 wherein said envelope has a plurality of deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along the major part of the length thereof,

each said deformation having a finite minimum depth throughout its entire length exclusive of its ends and varying in depth from said minimum at portions thereof along the length of the envelope, at least a portion of said are stream discharge following the curved path of said deformations along the length of the envelope and also being deflected from the envelope central axis in accordance with the variations in depths of the deformations.

4. A fluorescent lamp as in claim 3 wherein the respective variations in the depths of the portions of the deformations are substantially continuous.

5. The fluorescent lamp of claim 1 wherein said curved path is described by a helix.

6. A lamp as set forth in claim 5 wherein the depth of the deformation varies in accordance with a predetermined recurring function.

7. A fluorescent lamp as in claim 1 wherein the width of the deformation increases and the depth of the deformation decreases.

8. A fluorescent lamp comprising:

an elongated generally tubular envelope formed with a deformation in its outer wall in a curved path of finite radius around the central axis of the envelope and along a portion of the length thereof, said deformation varying substantially continuously in depth over portions thereof throughout the length of the envelope where the deformation exists,

a quantity of an ionizable material within said envelope, and

electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said are stream discharge following the curved path of said deformation along the length of the envelope and also being deflected from the envelope central axis in accordance with the varying depth of the deformation.

9. A lamp as set forth in claim 8 wherein the depth of the deformation varies periodically in accordance with a predetermined function.

10. A fluorescent lamp as in claim 8 wherein said envelope has a plurality of deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along a portion of the length thereof. each said deformation varying in depth in a substantially continuous manner at portions thereof along the length of the envelope where the deformations exists. at least a portion of said are stream discharge following the curved path of said deformations along the length of the envelope and also being deflected from the envelope central axis in accordance with the variations in depths of the deformations.

11. A fluorescent lamp as in claim 10 wherein the depths of the deformations vary in predetermined patterns so that the depth of at least one deformation is increasing while the depth of at least one other deformation is decreasing to produce a substantially constant perimeter to area ratio for the envelope cross section at substantially any point therealong.

12. A fluorescent lamp as in claim 8 wherein the width of a respective deformation increases as its depth decreases.

13. A fluorescent lamp comprising;

an elongated generally tubular envelope formed with a deformation in its outer wall in a curved path generally around and along the central axis of the envelope and along a portion of the length thereof, said deformation varying in depth at portions thereof along the length of the envelope,

a quantity of an ionizable material within said envelope, and

electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said are stream discharge following the curved path of said deformation along the length of the envelope and also being deflected from the envelope central axis in accordance with the variation in depth of the deformation.

14. A fluorescent lamp as in claim 13 wherein said deformation exists along a substantial portion of the length of the envelope and varies substantially continuously in depth over portions thereof.

15. A lamp as set forth in claim 14 wherein the depth of the deformation varies periodically in accordance with a predetermined function.

16. A fluorescent lamp comprising:

an elongated generally tubular envelope formed with a pair of deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along a portion of the length thereof, each said deformation varying in depth in a predetermined manner whereby the depth of one is increasing as the depth of the other is decreasing.

a quantity of an ionizable material within said envelope. and

electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said are stream discharge following the curved path of said deformations along the length of the envelope and also being deflected from the envelope central axis in accordance with the variations in depths of the deformations.

17. A fluorescent lamp as set forth in claim 16 wherein the depths of the deformations are varied to maintain a substantially constant perimeter to area ratio for the envelope cross section at substantially any point therealong where the deformations exists.

18. A fluorescent lamp as set forth in claim 17 wherein the depth of each deformation varies periodically in accordance with the same predetermined function.

19. A fluorescent lamp as set forth in claim 16 wherein the curved path each deformation follows is generally in the form of a helix.

20. A fluorescent lamp comprising:

an elongated generally tubular envelope formed with a pair of similar deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along a portion of the length thereof, each said deformation varying in depth between a minimum and a maximum value a plurality of times over its length in a predetermined manner and having a predetermined constant in-phase relationship with the other deformation, the cross section of the envelope changing in shape in accordance with the similar changes in the depth of the two deformations and thereby changing in area along the length where the said pair of deformations exist,

a quantity of an ionizable material within said envelope, and

electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said are stream discharge following the curved path of said deformations along the length of the envelope.

21. A fluorescent lamp as in claim 20 wherein each of said deformations varies in the form of a helix. 

2. A lamp as set forth in claim 1 wherein the depth of the deformation varies in accordance with a predetermined recurring function.
 3. A fluorescent lamp as in claim 1 wherein said envelope has a plurality of deformations in its outer wall, each deformation lying in a separate curved path arouNd the central axis of the envelope and along the major part of the length thereof, each said deformation having a finite minimum depth throughout its entire length exclusive of its ends and varying in depth from said minimum at portions thereof along the length of the envelope, at least a portion of said arc stream discharge following the curved path of said deformations along the length of the envelope and also being deflected from the envelope central axis in accordance with the variations in depths of the deformations.
 4. A fluorescent lamp as in claim 3 wherein the respective variations in the depths of the portions of the deformations are substantially continuous.
 5. The fluorescent lamp of claim 1 wherein said curved path is described by a helix.
 6. A lamp as set forth in claim 5 wherein the depth of the deformation varies in accordance with a predetermined recurring function.
 7. A fluorescent lamp as in claim 1 wherein the width of the deformation increases and the depth of the deformation decreases.
 8. A fluorescent lamp comprising: an elongated generally tubular envelope formed with a deformation in its outer wall in a curved path of finite radius around the central axis of the envelope and along a portion of the length thereof, said deformation varying substantially continuously in depth over portions thereof throughout the length of the envelope where the deformation exists, a quantity of an ionizable material within said envelope, and electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said arc stream discharge following the curved path of said deformation along the length of the envelope and also being deflected from the envelope central axis in accordance with the varying depth of the deformation.
 9. A lamp as set forth in claim 8 wherein the depth of the deformation varies periodically in accordance with a predetermined function.
 10. A fluorescent lamp as in claim 8 wherein said envelope has a plurality of deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along a portion of the length thereof, each said deformation varying in depth in a substantially continuous manner at portions thereof along the length of the envelope where the deformations exists, at least a portion of said arc stream discharge following the curved path of said deformations along the length of the envelope and also being deflected from the envelope central axis in accordance with the variations in depths of the deformations.
 11. A fluorescent lamp as in claim 10 wherein the depths of the deformations vary in predetermined patterns so that the depth of at least one deformation is increasing while the depth of at least one other deformation is decreasing to produce a substantially constant perimeter to area ratio for the envelope cross section at substantially any point therealong.
 12. A fluorescent lamp as in claim 8 wherein the width of a respective deformation increases as its depth decreases.
 13. A fluorescent lamp comprising; an elongated generally tubular envelope formed with a deformation in its outer wall in a curved path generally around and along the central axis of the envelope and along a portion of the length thereof, said deformation varying in depth at portions thereof along the length of the envelope, a quantity of an ionizable material within said envelope, and electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said arc stream discharge following the curved path of said deformation along the length of the envelope and also being deflected from the envelope central axis in accordance with the variation in depth of the deformation.
 14. A fluorescent lamp as in claim 13 wherein said deformation exists along a substantial portion of the leNgth of the envelope and varies substantially continuously in depth over portions thereof.
 15. A lamp as set forth in claim 14 wherein the depth of the deformation varies periodically in accordance with a predetermined function.
 16. A fluorescent lamp comprising: an elongated generally tubular envelope formed with a pair of deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along a portion of the length thereof, each said deformation varying in depth in a predetermined manner whereby the depth of one is increasing as the depth of the other is decreasing, a quantity of an ionizable material within said envelope, and electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said arc stream discharge following the curved path of said deformations along the length of the envelope and also being deflected from the envelope central axis in accordance with the variations in depths of the deformations.
 17. A fluorescent lamp as set forth in claim 16 wherein the depths of the deformations are varied to maintain a substantially constant perimeter to area ratio for the envelope cross section at substantially any point therealong where the deformations exists.
 18. A fluorescent lamp as set forth in claim 17 wherein the depth of each deformation varies periodically in accordance with the same predetermined function.
 19. A fluorescent lamp as set forth in claim 16 wherein the curved path each deformation follows is generally in the form of a helix.
 20. A fluorescent lamp comprising: an elongated generally tubular envelope formed with a pair of similar deformations in its outer wall, each deformation lying in a separate curved path around the central axis of the envelope and along a portion of the length thereof, each said deformation varying in depth between a minimum and a maximum value a plurality of times over its length in a predetermined manner and having a predetermined constant in-phase relationship with the other deformation, the cross section of the envelope changing in shape in accordance with the similar changes in the depth of the two deformations and thereby changing in area along the length where the said pair of deformations exist, a quantity of an ionizable material within said envelope, and electrode means at each end of said envelope for establishing an arc stream discharge of the ionizable material therebetween, at least a portion of said arc stream discharge following the curved path of said deformations along the length of the envelope.
 21. A fluorescent lamp as in claim 20 wherein each of said deformations varies in the form of a helix. 